Patient QA Breathing Phantom with Interchangeable Male-Female Chest: (M)ADAM
Abstract
Purpose
To upgrade the ADAM breathing phantom to include a female version, MADAM, featuring a thoracic cavity with breasts and a realistically-shaped heart. This design enables verification of breast radiotherapy treatments, broadening its application in patient-specific quality assurance (QA).
Methods
(M)ADAM is a 3D-printed torso phantom with embedded ribs and spinal cord, designed for 4D-imaging, dose delivery, gating and tracking of moving lesions. MADAM comprises interchangeable breasts of different sizes, whose density was selected to simulate human breast. Breasts, chest, and heart are sectioned to accommodate radiochromic film to compare planned and measured dose distributions. Vertical motion is driven by two synchronized motors, allowing different respiratory signals, including free breathing (FB) and deep inspiration breath hold (DIBH). Motion repeatability and reproducibility were assessed using laser triangulation sensors (1μm accuracy, 25Hz sampling), recording motor steps over 15 minutes for each signal and reacquiring the signals two months later. Left-breast 3DCRT treatment (40Gy/15fractions, tangential beams) was delivered as a representative use case for QA.
Results
Motion measurements demonstrated excellent temporal and spatial repeatability, with standard deviations below 0.02 s and 0.08 mm, respectively, for all tested signals, while reproducibility was assessed respectively within 0.01 s and 0.2 mm. CT# measurements (-90 to -70 HU) allow to define the 3D-printed breasts fully compatible with human mammalian tissue (-90 to -50 HU). Measured dose distributions meaningfully overlapped with the breast planning target volume. Maximum heart dose was below 80 cGy, consistent with treatment planning system calculations, supporting future studies on heart dose sensitivity to breathing variations.
Conclusion
(M)ADAM represents a significant upgrade of ADAM, supporting both FB and DIBH and enabling comprehensive end-to-end QA for breast treatments. Its tissue equivalency is crucial to accurately simulate clinical dose distributions. Its ability to reproduce arbitrary respiratory patterns makes it a versatile, professional, and cost-effective multipurpose phantom.